Weight and Balance

  • The Weight and Balance of this aircraft is a little off... For example, the Pilot/Copilot weight should be located ahead of the empty weight CG, and cause the loaded aircraft CG to move forward. And the fuel tanks should be behind the empty CG, and cause the loaded aircraft CG to move aft.

    Here are some modified weight and balance settings that are much closer to those found in the POH...

    ;station_load.0 =170, 0.096221, -0.901377, 1.599602, P1, 0
    ;station_load.1 =0, 0.096221, 0.9, 1.6, P2 (170), 0
    ;station_load.2 =0, -2, -0.8, 1.4, Passenger(170), 0
    ;station_load.3 =0, -2, 0.8, 1.4, Passenger(170), 0
    ;station_load.4 =0, -4.6, 0, 0.7, Luggage(200), 0

    station_load.0 =170, 1.05, -0.9, 1.2, P1, 0
    station_load.1 =0, 1.05, 0.9, 1.2, P2 (170), 0
    station_load.2 =0, -2.08, -0.8, 1.0, Passenger(170), 0
    station_load.3 =0, -2.08, 0.8, 1.0, Passenger(170), 0
    station_load.4 =0, -4.14, 0, 0.5, Luggage(200), 0

    ;LeftMain = 0.167, -4.5, 0.6, 38.5, 2.5
    ;RightMain = 0.167, 4.5, 0.6, 38.5, 2.5

    LeftMain = -0.15, -4.5, 0.6, 38.5, 2.5
    RightMain = -0.15, 4.5, 0.6, 38.5, 2.5

    EDIT: The vertical positions of the pilots and passengers have now also been lowered by 4.8 inches (0.4 ft.) to a more realistic location.

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  • Just to take your pilot adjustments - this is where you have placed the pilots' weight:

    This is where I have placed the pilots' weight:

    The fuel adjustment is minimal, but could probably work.

    Regarding the empty weight CG position, the 'Datum' referred to in the sim is the model datum and not the same datum as in the POH. For comparison, below are the EW CG position as I have set it up in the sim and as it is in the POH:

    The other thing to bear in mind is that this sim still suffers from the CG problem of the previous sims - if it is set a touch too close to the main gear, the aircraft falls through the surface and pirouettes around uncontrollably!

    I think that's close enough, so whilst I agree that there is leeway for movement with the fuel tanks the other points will be remaining where they are.

  • @Delta558 , Thanks for taking the time to evaluate my recommended changes...

    I arrived at these values by studying the POH Weight and Balance data, and I am fully aware that the reference datum and CG arms used in the POH charts are not the same as the Datum used in the simulated aircraft model. However, assuming the sim model was created to scale, the distances between the various arm locations should still be the same. For example, the relative distances between the CG arms of the front seat pilot/copilot and the rear seat passengers, or the fuel tanks or baggage area should be the same number of inches in both the sim model and the POH charts...

    The POH also specifies the CG arm locations of the main gear (109.7) and the wing leading edge (78.4). The Pilot's CG arm (80.5) is only 2.1 inches behind the leading edge, which is about where your screen shot shows my setting to be. While this may visually look too far forward, compared with some other aircraft, it accurately matches the actual aircraft specs... Keep in mind that this is a four seat aircraft, and with no rear passengers or baggage the CG will be close to the forward limit. Also, based on your screen shot, it looks to me like the Pilot/Copilot seats (and the pilots) are in their rear most position, and not adjusted to the actual correct flying position. And, the actual center of gravity for a seated pilot/copilot is not at his shoulder, but farther forward due to his extended legs.

    I calculated all of my recommended settings by using the Main Gear CG arm location from the POH (109.7) and the sim model gear location (-1.38) as a common known reference point, and then calculated all of the other CG arm locations relative to that point.

    I agree with your conclusion about the empty weight CG comparison... and I did not recommend any changes to that value.

    I have been test flying the aircraft with these new weight and balance settings for several days now, with different aircraft load combinations, and it seems to perform very well... My compliments to the entire JF team for creating such an outstanding aircraft!

    Screenshot 2021-04-12 144818.jpg

    Screenshot 2021-04-12 144844.jpg

  • @Delta558 said in Weight and Balance:

    This is where I have placed the pilots' weight:

    If the dot in this picture also shows the vertical location of the pilot and passenger weights, it should be moved down significantly to his actual center of gravity, which is closer to his belly button... Setting the vertical position of the pilot and passenger weights too high will raise the loaded aircraft CG and adversely affect the roll stability of the aircraft.

    EDIT: I just lowered the pilot and passenger vertical weight positions by 4.8 inches (-0.4 ft.) and test flew the aircraft again... This change significantly improves the roll stability of the aircraft.

  • @Delta558 , This loading chart from the POH shows how the aircraft CG should change (forward or aft) as the pilot/copilot, baggage and fuel weights are added...
    Screenshot 2021-04-13 052338.jpg

  • @RetiredMan93231 Longitudinal only - I used one of the Gizmos that still works and just entered the longitudinal position!

  • @Delta558 said in Weight and Balance:

    @RetiredMan93231 Longitudinal only - I used one of the Gizmos that still works and just entered the longitudinal position!

    Based on the screen shot of the pilots, I think their vertical CG should be about the same as the Engine/Prop vertical CG (1.2), since their legs are below the prop center line and the rest of their body is above it... And, the rear passengers should be about 1.0. This significantly improves the roll stability of the aircraft!

  • In addition to the changes recommended above to correct the CG Arm locations of the Pilots, Passengers and Baggage, the current CG limit range is also incorrect and should be updated.

    The following recommended change to the flight_model.cfg file, in addition to the previous changes, will more closely match the actual CG limits and CG range found in the aircraft POH...

    CG_forward_limit =0.14
    CG_aft_limit =0.3 ;0.4